Oil Recovery Process Using an Oil Recovery Composition of Aqueous Salt Solution and Dilute Polymer for Carbonate Reservoirs

ABSTRACT

An oil recovery composition of an aqueous solution of one or more salts and dilute polymer and processes for enhanced oil recovery using the oil recovery composition are provided. An oil recovery composition may include an aqueous solution of one or more salts having a salinity of about 4000 parts-per-million (ppm) total dissolved solids (TDS) to about 8000 ppm TDS and a polymer having a concentration of 250 ppm to 750 ppm. The one or more salts may include at least one of sodium chloride (NaCl), calcium chloride (CaCl2), magnesium chloride (MgCl2), sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4). The polymer may include a copolymer of acrylamide and acrylamido tertiary butyl sulfonate (ATBS). The oil recovery compositions provided may be suited for enhancing oil recovery in carbonate reservoirs having in situ oil viscosities less than 3 centipoise (cP).

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional of and claims priority from U.S.Non-Provisional application Ser. No. 16/686,769, filed Nov. 18, 2019,and titled “OIL RECOVERY PROCESS USING AN OIL RECOVERY COMPOSITION OFAQUEOUS SALT SOLUTION AND DILUTE POLYMER FOR CARBONATE RESERVOIRS,”which is a continuation of and claims priority from U.S. Non-Provisionalapplication Ser. No. 16/273,956, filed Feb. 12, 2019, and titled “OILRECOVERY PROCESS USING AN OIL RECOVERY COMPOSITION OF AQUEOUS SALTSOLUTION AND DILUTE POLYMER FOR CARBONATE RESERVOIRS,” which is acontinuation-in-part of and claims priority from U.S. Non-Provisionalapplication Ser. No. 15/358,435, filed Nov. 22, 2016, and titled “OILRECOVERY PROCESS USING AN OIL RECOVERY COMPOSITION OF AQUEOUS SALTSOLUTION AND DILUTE POLYMER FOR CARBONATE RESERVOIRS,” which claimspriority from U.S. Provisional Application No. 62/280,446, filed Jan.19, 2016, and titled “OIL RECOVERY PROCESS USING AN OIL RECOVERYCOMPOSITION OF SMART WATER AND DILUTE POLYMER FOR CARBONATE RESERVOIRS,”each of which are incorporated by reference in their entirety forpurposes of United States patent practice.

BACKGROUND Field of the Disclosure

Embodiments of the disclosure generally relate to formation treatmentfluids and, more specifically, to enhanced oil recovery fluids.

Description of the Related Art

The use of enhanced oil recovery (EOR) processes has greatly benefitedthe oil and gas industry by increasing the production of problematic andunderperforming hydrocarbon bearing wells and fields. The EOR processesused in modern oil and gas operations may include chemical,hydrochemical, thermal, fluid/superfluid and microbial based processesas well as the relatively recent plasma-pulse technology (PPT). Waterinjection (alternatively referred to as water flooding) has been widelyused to increase the conductivity or flow of liquid hydrocarbons insubterranean reservoir treated using EOR techniques. The water sourcemay be derived from freshwater, (for example, aquifers or surface water)as well as saltwater/brackish sources (for example, river/sea watermixtures).

SUMMARY

The use of water flooding processes may be used for EOR operations incarbonate reservoirs. Such water flooding processes involve an ion-based(that is, salt-based) modification to an injectable water fraction. Inaddition, such water flooding processes may be generally regarded asenvironmentally safe. Further such water flooding may improvemicroscopic sweep efficiency and release more oil from reservoir pores.However, such water flooding may be mobility constrained due toinsufficient injection water viscosities, resulting in poor sweepefficiencies at the reservoir scale.

Embodiments of the disclosure generally relate to an oil recoverycomposition of an aqueous solution of one or more salts with a salinityof about 4,000 parts-per-million (ppm) total dissolved solids (TDS) toabout 8,000 ppm TDS and dilute polymer for improved oil recovery from ahydrocarbon containing carbonate reservoir formation. In one embodiment,an oil recovery composition is provided having an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS and a polymer having a concentration of 250 ppm to 750ppm. The one or more salts may include at least one of sodium chloride(NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), sodiumsulfate (Na₂SO₄) and magnesium sulfate (MgSO₄). In some embodiments, theoil recovery composition consists of the aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDSand the polymer having a concentration of 250 ppm to 750 ppm.

In some embodiments, the aqueous solution of the oil recoverycomposition includes one or more ions of at least one of sodium,calcium, magnesium, sulfate, and chloride. In some embodiments, thepolymer of the oil recovery composition is a copolymer of acrylamide andacrylamido tertiary butyl sulfonate (ATBS).

In another embodiment, a method for enhancing oil recovery in ahydrocarbon containing carbonate reservoir formation is provided. Themethod includes injecting a first slug of a first aqueous solution ofone or more salts and metal oxide nanoparticles into the carbonatereservoir formation. The first aqueous solution has a salinity of about4,000 ppm TDS to about 8,000 ppm TDS. The one or more salts of the firstaqueous solution include at least one of sodium chloride (NaCl), calciumchloride (CaCl2), magnesium chloride (MgCl2), sodium sulfate (Na2SO4)and magnesium sulfate (MgSO4). In some embodiments, the metal oxidenanoparticles have a concentration in the range of 0.05 weight (wt) % to0.5 wt %. In other embodiments, the metal oxide nanoparticles have aconcentration in the range of 0.01 wt % to 0.05 wt %. In someembodiments, the first aqueous solution includes a surfactant. In someembodiments, the surfactant has a concentration in the range of 0.05weight (wt) % to 0.5 wt %. In other embodiments, the surfactant has aconcentration in the range of 0.01 wt % to 0.05 wt %. In someembodiments, the surfactant is an anionic surfactant, a cationicsurfactant, a nonionic surfactant, an amphoteric surfactant, and acatanionic surfactant, or any combination thereof.

The method further includes injecting a second slug of an oil recoverycomposition into the reservoir formation after injecting the first slug.The oil recovery composition includes an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDSand a polymer having a concentration of 250 ppm to 750 ppm. The secondone or more salts of the second aqueous solution include at least one ofsodium chloride (NaCl), calcium chloride (CaCl2), magnesium chloride(MgCl2), sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4).

In some embodiments, the method includes injecting a third solution intothe carbonate reservoir formation after injecting the second slug. Insome embodiments, the method includes recovering displaced oil from thecarbonate reservoir formation. In some embodiments, the third solutionincludes seawater. In some embodiments, the third solution includesproduced water. In some embodiments, the third solution comprises one ormore ions, the one or more ions comprising at least one of: sodium,calcium, magnesium, and sulfate. In some embodiments, injecting a thirdsolution into the carbonate reservoir formation includes continuouslyinjecting the third solution into the carbonate reservoir formation atan injection rate. In some embodiments, the first slug of the firstaqueous solution has a pore volume of in the range of 0.3 to 0.5 of thecarbonate reservoir to be treated. In some embodiments, the second slugof the oil recovery composition has a pore volume in the range of 0.5 to1.0 of the carbonate reservoir to be treated. In some embodiments, thefirst aqueous solution includes one or more ions of at least one ofsodium, calcium, magnesium, sulfate, and chloride. In some embodiments,the second aqueous solution includes one or more ions of at least one ofsodium, calcium, magnesium, sulfate, and chloride. In some embodiments,the polymer of the oil recovery composition includes a copolymer ofacrylamide and acrylamido tertiary butyl sulfonate (ATBS).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescriptions, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of thedisclosure and are therefore not to be considered limiting of thedisclosure's scope as it can admit to other equally effectiveembodiments.

FIG. 1 is a schematic illustrating improved oil recovery from carbonatereservoirs using an oil recovery composition in accordance with anembodiment of the disclosure;

FIG. 2 is a plot of a ratio of aqueous salt solution viscosity overseawater viscosity vs polymer concentration in ppm for a first exampleaqueous salt solution in accordance with an embodiment of thedisclosure;

FIG. 3 is a plot of a ratio of aqueous salt solution viscosity overseawater viscosity vs polymer concentration in ppm for a second exampleaqueous salt solution in accordance with an embodiment of thedisclosure;

FIGS. 4-6 are flowcharts of processes for enhancing oil recovery fromcarbonate reservoirs using an oil recovery composition of an aqueoussalt solution of one or more salts and dilute polymer in accordance withembodiments of the disclosure; and

FIGS. 7 and 8 are flowcharts of processes for enhancing oil recoveryfrom carbonate reservoirs using an aqueous solution of one or more saltshaving a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) and metal oxidenanoparticles, and an oil recovery composition of an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer in accordance with embodiments of the disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully with referenceto the accompanying drawings, which illustrate embodiments of thedisclosure. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the illustratedembodiments set forth in the disclosure. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the disclosure to those skilled in the art.

As used in the disclosure, an aqueous solution of one or more saltssuitable for enhancing oil recovery in carbonate reservoirs may have asalinity in the range of about 5,000 parts-per-million (ppm) totaldissolved solids (TDS) to about 6,000 ppm TDS, such that the aqueoussolution includes a concentration of one or more of the following ionssuitable for enhancing oil recovery: sodium, calcium, magnesium,sulfate, and chloride ions. For example, a an aqueous solution mayinclude one or more of the following salts suitable for enhancing oilrecovery: sodium chloride (NaCl), calcium chloride (CaCl₂), magnesiumchloride (MgCl₂), sodium sulfate (Na₂SO₄) and magnesium sulfate (MgSO₄).

As used in the disclosure, “in situ” refers to an event or occurrencewithin a hydrocarbon reservoir including but not limited tomethodologies, techniques and chemical reactions for enhancinghydrocarbon recovery from carbonate reservoirs. As used in thedisclosure, the term “ppm” refers to parts-per-million by mass unlessotherwise indicated.

As shown in FIG. 1, embodiments of the disclosure include an oilrecovery composition formed from an aqueous solution of one or moresalts with a salinity of about 5,000 ppm to about 6,000 ppm and dilutepolymer that has improved oil recovery performance (Recovery >X) overthe oil recovery obtained using only the an aqueous solution of one ormore salts (Recovery=X). The polymer concentrations in the oil recoverycomposition provide an increase in viscosity of the aqueous solution andthus provide mobility control and improve the macroscopic sweepefficiency at reservoir scale. These improvements add to the microscopicsweep efficiency obtained from the aqueous solution alone tosignificantly boost the oil recovery performance in carbonatereservoirs. Additionally, the lower salinities and specific ions (forexample, sulfates) in the aqueous solution also increase theviscosifying characteristics of enhanced oil recovery polymers used.Accordingly, relatively greater viscosities can be achieved with suchoil recovery compositions using the aqueous solutions described in thedisclosure when compared to seawater used in typical water floods.Consequently, a greater oil recovery may be obtained as compared toconventional flooding compositions, resulting in improved economics(that is, lower cost) for oil recovery in carbonate reservoirs.

For example, in some embodiments an oil recovery composition may includean aqueous solution of one or more salts having a salinity of about4,000 ppm TDS to about 8,000 ppm TDS and an anionic oil recovery polymerhaving a polymer concentration of about 250 ppm to about 750 ppm. Insome embodiments, the one or more salts may include at least one of:sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride(MgCl₂), sodium sulfate (Na₂SO₄) and magnesium sulfate (MgSO₄). In someembodiments, the aqueous solution of one or more salts may include atleast one or more of the following ions: sodium, calcium, magnesium, orsulfates. In some embodiments, the polymer may be a copolymer ofacrylamide and acrylamido tertiary butyl sulfonate (ATBS).

Embodiments of the disclosure also include processes for enhancing oilrecovery in carbonate reservoirs using an oil recovery composition of anaqueous solution of one or more salts with a salinity of about 4,000 ppmTDS to about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000ppm TDS) and dilute polymer. In some embodiments, a process forenhancing oil recovery may include injecting a small slug of an oilrecovery composition of an aqueous solution of one or more salts with asalinity of about 4,000 ppm TDS to about 8,000 ppm TDS (for example,5,000 ppm TDS to about 6,000 ppm TDS) and dilute polymer having a porevolume (PV) of at least about 0.3 into a reservoir formation, followedby continuously injecting an aqueous solution of one or more saltshaving a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) into the reservoirformation. In some embodiments, a process for enhancing oil recovery mayinclude injecting a slug of an aqueous solution of one or more saltswith a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) and metal oxidenanoparticles in an amount in the range of 0.05 weight (wt) % to 0.5 wt% and having a PV in the range of about 0.3 to about 0.5 of thereservoir formation, followed by injecting a slug of an oil recoverycomposition of the aqueous solution and a dilute polymer having a PV inthe range of 0.5 to 1.0 of the reservoir formation. After injecting theslug of the oil recovery composition, the process may includecontinuously injecting another aqueous solution of one or more salts,seawater, or produced water into the reservoir formation or alternatingfrom among these solutions.

The following examples are included to demonstrate embodiments of thedisclosure. It should be appreciated by those of skill in the art thatthe techniques and compositions disclosed in the example which followsrepresents techniques and compositions discovered by the inventors tofunction well in the practice of the disclosure, and thus can beconsidered to constitute preferred modes for its practice. However,those of skill in the art should, in light of the present disclosure,appreciate that many changes can be made in the specific embodimentswhich are disclosed and still obtain a like or a similar result withoutdeparting from the spirit and scope of the disclosure.

In one non-limiting example, an oil recovery composition was formedusing a first aqueous solution (“Aqueous Salt Solution 1”) having asalinity of about 5761 ppm total dissolved solids (TDS) and having ionconcentrations of 1,824 ppm sodium, 65 ppm calcium, 211 ppm magnesium,429 ppm sulfates and 3,220 ppm chloride ions. In a second non-limitingexample, an oil recovery composition was formed using a second aqueoussolution (“Aqueous Salt Solution 2”) having a salinity of about 5761 ppmTDS with an ion concentration of 1,865 ppm sodium and 3,896 ppmsulfates. Thus, Aqueous Salt Solution 1 includes calcium, magnesium, andsulfate ions and Aqueous Salt Solution 2 only includes sulfates. Asexplained further in the disclosure, the presence of ions such ascalcium, magnesium, and sulfates may initiate interactions at the porescale to further enhance oil recovery in a carbonate reservoir.

In one non-limiting example, a commercially available copolymer ofacrylamide (AM) and acrylamido tertiary butyl sulfonate (ATBS, FlopaamAN-125 manufactured by SNF Floerger of Andrézieux, France (referred toas “AN-125” polymer), was added to each example aqueous solution inconcentrations of 250 ppm, 500 ppm, and 750 ppm, and the viscosities ofthe modified aqueous solutions were measured at three differenttemperatures of 25° C., 40° C., and 60° C. and at a shear rate of 6.81sec⁻¹. The measured viscosities of the modified aqueous solutions werecompared to seawater (seawater having a salinity of about 57,610 ppm)viscosities at the same polymer concentration and temperature. Theviscosities of Aqueous Salt Solution 1 and Aqueous Salt Solution 2 andtheir comparison with seawater viscosities at polymer concentrations of0 ppm, 250 ppm, 500 ppm, and 750 ppm, and at the three differenttemperatures are shown in Tables 1-3. The percentage change summarizedin these Tables indicate a percentage increase in the viscosities of thetested aqueous solutions when compared to seawater viscosity at the samepolymer concentration:

TABLE 1 Seawater and Aqueous Solution Viscosities with Dilute Polymer at25° C. 0 250 % 500 % 750 % Composition ppm ppm Change ppm Change ppmChange Average Seawater 1.04 1.4 0.0 2.6 0.0 3.6 0.0 0.0 Aqueous Salt0.96 1.9 35.7 3.4 30.8 4.2 16.7 27.7 Solution 1 Aqueous Salt 0.96 2.578.6 4.3 65.4 4.7 30.6 58.2 Solution 2

TABLE 2 Seawater and Aqueous Solution Viscosities with Dilute Polymer at40° C. 0 250 % 500 % 750 % Composition ppm ppm Change ppm Change ppmChange Average Seawater 0.88 1.1 0.0 2.1 0.0 2.9 0.0 0.0 Aqueous Salt0.81 1.2 9.1 2.7 28.6 3.2 10.3 16.0 Solution 1 Aqueous Salt 0.81 1.972.7 3.3 57.1 3.7 27.6 52.5 Solution 2

TABLE 3 Seawater and Aqueous Solution Viscosities with Dilute Polymer at60° C. 0 250 % 500 % 750 % Composition ppm ppm Change ppm Change ppmChange Average Seawater 0.67 0.8 0.0 1.4 0.0 2.0 0.0 0.0 Aqueous Salt0.62 0.9 12.5 2.0 42.9 2.4 20.0 25.1 Solution 1 Aqueous Salt 0.62 1.8125.0 2.6 85.7 2.8 40.0 83.6 Solution 2

FIG. 2 depicts a plot 200 illustrating the viscosity improvements ofAqueous Salt Solution 1 as compared to seawater at the various polymerconcentrations of 250 ppm, 500 ppm, 750 ppm. As shown in FIG. 2, theY-axis 202 corresponds to the ratio of tested aqueous solution viscosityover seawater viscosity, and the X-axis 204 corresponds to the polymerconcentration in ppm. FIG. 2 depicts data points corresponding to apolymer concentration of 250 ppm, data points corresponding to a polymerconcentration of 500 ppm, and data points corresponding to polymerconcentrations of 750 ppm at the three different temperatures of 25° C.,40° C. and 60° C. (as indicated by the legend 206).

Similarly, FIG. 3 depicts a plot 300 illustrating the viscosityimprovements of Aqueous Salt Solution 2 as compared to seawater at thevarious polymer concentrations of 250 ppm, 500 ppm, 750 ppm. As shown inFIG. 3, the Y-axis 302 corresponds to the ratio of tested aqueoussolution viscosity over seawater viscosity, and the X-axis 304corresponds to the polymer concentration in ppm. As shown in the legend306, FIG. 3 depicts data points corresponding to a polymer concentrationof 250 ppm, data points corresponding to a polymer concentration of 500ppm, and data points corresponding to polymer concentrations of 750 ppmat the three different temperatures of 25° C., 40° C. and 60° C.

As shown in Tables 1-3 and as illustrated in FIGS. 2 and 3, both testedaqueous solutions developed about 1.5 to 2.0 times greater viscositieswith a 250 ppm polymer concentration and 3 to 4 times greaterviscosities with 500 ppm polymer concentrations when compared toseawater alone. Moreover, the incremental viscosities observed in bothtested aqueous solutions at the various polymer concentrations wereabout 25 to 50% greater than seawater having the various polymerconcentrations.

Additionally, as shown in Tables 1-3, the incremental viscosities ofAqueous Salt Solution 2 were about 2 to 3 times greater than AqueousSalt Solution 1 likely due to the reduced interaction of sodium ion withthe AN-125 polymer due to the increased concentration of sulfates inAqueous Salt Solution 2. Thus, as shown supra, the addition of polymerto tested aqueous solutions in dilute concentrations results inviscosities suitable for enhanced oil recovery and provides improvedpolymer viscosifying characteristics due to favorable interactions ofboth low salinity and specific ions such as sulfates present in thetested aqueous solutions.

In some embodiments, an oil recovery composition of an aqueous solutionof one or more salts with a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer may be suitable for light oil recovery with in situreservoir oil viscosities of less than 10 cP. In some embodiments, theoil recovery composition of an aqueous solution of one or more saltswith a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) may be suitable for lightoil recovery with in situ reservoir oil viscosities of less than 3 cP.

Embodiments of the disclosure may include oil recovery compositions thatinclude an aqueous solution of one or more salts with a salinity ofabout 4,000 ppm TDS to about 8,000 ppm TDS. In some embodiments, anaqueous solution may include one or more salts that include but are notlimited to sodium chloride (NaCl), calcium chloride (CaCl₂), magnesiumchloride (MgCl₂), sodium sulfate (Na₂SO₄) and magnesium sulfate (MgSO₄).Embodiments of the disclosure may include aqueous solutions having aconcentration of one or more ions that include but are not limited tosodium ions, sulfate ions, calcium ions, magnesium ions, and chlorideions. In some embodiments, an aqueous solution in the oil recoverycomposition may include dilute seawater (that is, seawater diluted toachieve a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS). Insome embodiments, the dilute seawater may include the addition of one ormore salts (for example, at least one of sodium chloride (NaCl), calciumchloride (CaCl₂), magnesium chloride (MgCl₂), sodium sulfate (Na₂SO₄)and magnesium sulfate (MgSO₄)). In some embodiments, an aqueous solutionof one or more salts in the improved oil recovery composition withdilute polymer may have a salinity of about 4,000 ppm TDS to about 8,000ppm TDS and may include about 400 ppm or greater sulfates and about 300ppm or less of calcium and magnesium together.

In some embodiments, an oil recovery composition described in thedisclosure may include metal oxide nanoparticles (that is particleshaving at least one dimension (for example diameter or length) in therange of 1 nanometer to 100 nanometers). In some embodiments, the metaloxide nanoparticles may include silicon dioxide (SiO₂), aluminum oxide(Al₂O₃) or both. In some embodiments, the oil recovery composition mayinclude metal oxide nanoparticles having a concentration in the range of0.05 weight (wt) % to 0.5 wt %. Accordingly, in some embodiments, an oilrecovery composition may include an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS(for example, about 5,000 ppm TDS to about 6,000 ppm TDS) according tothe criteria described in the disclosure, and metal oxide nanoparticleshaving a concentration in the range of 0.05 weight (wt) % to 0.5 wt %.In some embodiments, the oil recovery composition may include metaloxide nanoparticles having a concentration in the range of 0.01 weight(wt) % to 0.05 wt %. Accordingly, in some embodiments, an oil recoverycomposition may include an aqueous solution of one or more salts havinga salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (for example,about 5,000 ppm TDS to about 6,000 ppm TDS) according to the criteriadescribed in the disclosure, and metal oxide nanoparticles having aconcentration in the range of 0.01 weight (wt) % to 0.05 wt %.

In some embodiments, an oil recovery composition described in thedisclosure may include a surfactant. In some embodiments, the surfactantmay include an anionic surfactant, a cationic surfactant, a nonionicsurfactant, an amphoteric surfactant, and a catanionic surfactant, orany combination thereof. In some embodiments, the oil recoverycomposition may include a surfactant having a concentration in the rangeof 0.05 weight (wt) % to 0.5 wt %. Accordingly, in some embodiments, anoil recovery composition may include an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS(for example, about 5,000 ppm TDS to about 6,000 ppm TDS) according tothe criteria described in the disclosure, and a surfactant having aconcentration in the range of 0.05 weight (wt) % to 0.5 wt %. In someembodiments, an oil recovery composition may include an aqueous solutionof one or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, about 5,000 ppm TDS to about 6,000 ppm TDS)according to the criteria described in the disclosure, metal oxidenanoparticles having a concentration in the range of 0.05 weight (wt) %to 0.5 wt %, and a surfactant having a concentration in the range of0.05 weight (wt) % to 0.5 wt %. In some embodiments, the oil recoverycomposition may include a surfactant having a concentration in the rangeof 0.01 weight (wt) % to 0.05 wt %. Accordingly, in some embodiments, anoil recovery composition may include an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS(for example, about 5,000 ppm TDS to about 6,000 ppm TDS) according tothe criteria described in the disclosure, and a surfactant having aconcentration in the range of 0.01 weight (wt) % to 0.05 wt %. In someembodiments, an oil recovery composition may include an aqueous solutionof one or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, about 5,000 ppm TDS to about 6,000 ppm TDS)according to the criteria described in the disclosure, metal oxidenanoparticles having a concentration in the range of 0.01 weight (wt) %to 0.05 wt %, and a surfactant having a concentration in the range of0.01 weight (wt) % to 0.05 wt %.

Embodiments of the disclosure may include oil recovery compositions thatinclude suitable anionic enhanced oil recovery polymers diluted topolymer concentrations in the range of 250 ppm to 750 ppm when combinedwith an aqueous solution of one or more salts to form the oil recoverycompositions. These polymers may include but are not limited topolyacrylamides and copolymers of acrylamide. Such polymers may includebut are not limited to partially hydrolyzed polyacrylamides (HPAM),copolymers of ATBS and acrylamide. In some embodiments, such polymersmay be selected from the Flopaam AN series of polymers manufactured bySNF Floerger of Andrézieux, France.

Embodiments of the disclosure may include an oil recovery compositionthat includes an aqueous solution of one or more salts according to thecriteria described in the disclosure and a polymer in the range of 250ppm to 750 ppm. For example, embodiments of the disclosure may includean oil recovery composition that includes an aqueous solution of one ormore salts according to the criteria described in the disclosure and apolymer diluted to a concentration of about 250 ppm to about 500 ppm,about 250 ppm to about 400 ppm, about 250 ppm to about 300 ppm. In someembodiments, as described infra, an oil recovery composition of anaqueous solution of one or more salts having a salinity of about 4,000ppm TDS to about 8,000 ppm TDS and dilute polymer may be used incombination with another aqueous solution of one or more salts,seawater, produced water, and other oil recovery compositions of anaqueous solution of one or more salts and dilute polymer.

With the foregoing in mind, the oil recovery composition of an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and dilute polymer may be used to enhance oil recovery fromcarbonate reservoirs using the example injection sequences illustratedin FIGS. 4-6 and described infra. In such embodiments, the injection ofthe oil recovery composition of an aqueous solution of one or more saltshaving a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) and dilute polymer into ahydrocarbon containing carbonate reservoir formation according to theprocesses described infra results in increased hydrocarbon productionfrom the reservoir formation.

FIG. 4 depicts a process 400 for enhancing oil recovery using an oilrecovery composition of an aqueous solution of one or more salts havinga salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (for example,5,000 ppm TDS to about 6,000 ppm TDS) and dilute polymer in accordancewith an embodiment of the disclosure. As shown in FIG. 4, in someembodiments, a slug of an oil recovery composition of an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and dilute polymer may be injected or otherwise introduced into thecarbonate reservoir formation (block 402). As described supra, the oilrecovery composition may include an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS(for example, 5,000 ppm TDS to about 6,000 ppm TDS) and a polymer havinga concentration in the range of 250 ppm to 750 ppm. In some embodiments,the slug of an aqueous solution of one or more salts having a salinityof about 4,000 ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppmTDS to about 6,000 ppm TDS) and dilute polymer may have a PV of at least0.3 of the reservoir to be treated. Following the injection of the slugof the oil recovery composition, an aqueous solution of one or moresalts having a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS(for example, 5,000 ppm TDS to about 6,000 ppm TDS) may be continuouslyinjected into the carbonate reservoir formation (block 404). The aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) continuously injected into the reservoir may be the same aqueoussolution in the oil recovery composition or may be a different aqueoussolution. Finally, displaced oil may be recovered from the carbonatereservoir formation (block 406).

FIG. 5 depicts a process 500 for enhancing oil recovery from a carbonatereservoir formation using an oil recovery composition of an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and dilute polymer in accordance with another embodiment of thedisclosure. As shown in FIG. 5, in some embodiments, a slug of anaqueous solution of one or more salts having a salinity of about 4,000ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppm TDS to about6,000 ppm TDS) may be injected into the carbonate reservoir (block 502).Next, a slug of an oil recovery composition of an aqueous solution ofone or more salts and dilute polymer may be injected into the carbonatereservoir (block 504). As described supra, the oil recovery compositionmay include an aqueous solution of one or more salts having a salinityof about 4,000 ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppmTDS to about 6,000 ppm TDS) and a polymer having a concentration in therange of 250 ppm to 750 ppm. In some embodiments, the slug of oilrecovery composition may have a PV in the range of about 0.5 to about1.0 of the reservoir to be treated. Following the injection of the slugof aqueous solution of one or more salts and the slug of oil recoverycomposition, an aqueous solution of one or more salts having a salinityof about 4,000 ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppmTDS to about 6,000 ppm TDS) may be continuously injected into thecarbonate reservoir (block 506). Finally, displaced oil may be recoveredfrom the carbonate reservoir formation (block 508).

FIG. 6 depicts a process 600 for enhancing oil recovery from a carbonatereservoir formation using an oil recovery composition of an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and dilute polymer in accordance with another embodiment of thedisclosure. As shown in FIG. 6, in some embodiments, a slug of anaqueous solution of one or more salts having a salinity of about 4,000ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppm TDS to about6,000 ppm TDS) may be injected into the carbonate reservoir (block 602).Next, a slug of an oil recovery composition of an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer may be injected into the carbonate reservoir (block 604).As described supra, the oil recovery composition may include an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and a polymer having a concentration in the range of 250 ppm to 750ppm. In some embodiments, the slug of the aqueous solution and dilutepolymer may have a PV in the range of about 0.5 to about 1.0 of thereservoir to be treated. Following the injection of the slug of aqueoussolution and the slug of oil recovery composition, seawater or producedwater may be continuously injected into the carbonate reservoirformation (block 606). Finally, displaced oil may be recovered from thecarbonate reservoir formation (block 608).

In some embodiments, an oil recovery composition of an aqueous solutionof one or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS), metaloxide nanoparticles and, in some embodiments, a surfactant, may be usedto enhance oil recovery from carbonate reservoirs using the exampleinjection sequences illustrated in FIGS. 7 and 8 and described infra. Insuch embodiments, the injection of the oil recovery composition of anaqueous solution of one or more salts having a salinity of about 4,000ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppm TDS to about6,000 ppm TDS), metal oxide nanoparticles, and, in some embodiments, asurfactant, into a hydrocarbon containing carbonate reservoir formationaccording to the processes described infra results in increasedhydrocarbon production from the reservoir formation.

FIG. 7 depicts a process 700 for enhancing oil recovery from a carbonatereservoir formation using an aqueous solution of one or more saltshaving a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) and metal oxidenanoparticles, and an oil recovery composition of an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer, in accordance with another embodiment of the disclosure.As shown in FIG. 7, in some embodiments, a slug of an aqueous solutionof one or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) andmetal oxide nanoparticles may be injected into the carbonate reservoir(block 702). As described supra, the aqueous solution may include metaloxide nanoparticles having a concentration in the range of 0.05 weight(wt) % to 0.5 wt % or a concentration in the range of 0.01 wt % to 0.05wt %. In some embodiments, the aqueous solution may include a surfactanthaving a concentration in the range of 0.05 weight (wt) % to 0.5 wt % ora concentration in the range of 0.01 wt % to 0.05 wt %.

Next, a slug of an oil recovery composition of an aqueous solution ofone or more salts and dilute polymer may be injected into the carbonatereservoir (block 704). As described supra, the oil recovery compositionmay include an aqueous solution of one or more salts having a salinityof about 4,000 ppm TDS to about 8,000 ppm TDS (for example, 5,000 ppmTDS to about 6,000 ppm TDS), and a polymer having a concentration in therange of 250 ppm to 750 ppm. In some embodiments, the slug of oilrecovery composition may have a PV in the range of about 0.5 to about1.0 of the reservoir to be treated.

Following the injection of the slug of aqueous solution of one or moresalts and the slug of oil recovery composition, an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) may becontinuously injected into the carbonate reservoir (block 706). Finally,displaced oil may be recovered from the carbonate reservoir formation(block 708).

FIG. 8 depicts a process 800 for enhancing oil recovery from a carbonatereservoir formation using an aqueous solution of one or more saltshaving a salinity of about 4,000 ppm TDS to about 8,000 ppm TDS (forexample, 5,000 ppm TDS to about 6,000 ppm TDS) and metal oxidenanoparticles, and an oil recovery composition of an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer, in accordance with another embodiment of the disclosure.As shown in FIG. 8, in some embodiments, a slug of an aqueous solutionof one or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) andmetal oxide nanoparticles may be injected into the carbonate reservoir(block 802). As described supra, the aqueous solution may include metaloxide nanoparticles having a concentration in the range of 0.05 weight(wt) % to 0.5 wt % or a concentration in the range of 0.01 wt % to 0.05wt %. In some embodiments, the aqueous solution may include a surfactanthaving a concentration in the range of 0.05 weight (wt) % to 0.5 wt % ora concentration in the range of 0.01 wt % to 0.05 wt %.

Next, a slug of an oil recovery composition of an aqueous solution ofone or more salts having a salinity of about 4,000 ppm TDS to about8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppm TDS) anddilute polymer may be injected into the carbonate reservoir (block 804).As described supra, the oil recovery composition may include an aqueoussolution of one or more salts having a salinity of about 4,000 ppm TDSto about 8,000 ppm TDS (for example, 5,000 ppm TDS to about 6,000 ppmTDS) and a polymer having a concentration in the range of 500 ppm to 750ppm. In some embodiments, the slug of the aqueous solution and dilutepolymer may have a PV in the range of about 0.5 to about 1.0 of thereservoir to be treated. Following the injection of the slug of aqueoussolution and the slug of oil recovery composition, seawater or producedwater may be continuously injected into the carbonate reservoirformation (block 806). Finally, displaced oil may be recovered from thecarbonate reservoir formation (block 808).

Further modifications and alternative embodiments of various aspects ofthe disclosure will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the embodiments described inthe disclosure. It is to be understood that the forms shown anddescribed in the disclosure are to be taken as examples of embodiments.Changes may be made in the elements described in the disclosure withoutdeparting from the spirit and scope of the disclosure as described inthe following claims. Headings used in the disclosure are fororganizational purposes only and are not meant to be used to limit thescope of the description.

Ranges may be expressed in the disclosure as from about one particularvalue, to about another particular value or both. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value, to the other particular value, or both, along withall combinations within said range.

What is claimed is:
 1. An oil recovery composition, comprising: anaqueous solution of one or more salts having a salinity of 4000parts-per-million (ppm) total dissolved solids (TDS) to 8000 ppm TDS,the one or more salts comprising sodium sulfate (Na₂SO₄); and aplurality of metal oxide nanoparticles having a concentration in therange of 0.05 weight (wt) % to 0.5 wt %.
 2. The oil recovery compositionof claim 1, consisting of the aqueous solution of one or more saltshaving a salinity of 4000 parts-per-million (ppm) to 8000 ppm, the oneor more salts comprising sodium sulfate (Na₂SO₄); and the plurality ofmetal oxide nanoparticles having a concentration in the range of 0.05weight (wt) % to 0.5 wt %.
 3. The oil recovery composition of claim 1,wherein the aqueous solution comprises one or more ions, the one or moreions comprising at least one of: sodium, calcium, magnesium, andsulfate.
 4. The oil recovery composition of claim 1, wherein the metaloxide nanoparticles comprise silicon dioxide, aluminum oxide, or acombination thereof.
 5. The oil recovery composition of claim 1, whereinthe first aqueous solution comprises a surfactant having a concentrationin the range of 0.05 weight (wt) % to 0.5 wt %.
 6. The oil recoverycomposition of claim 5, wherein the surfactant comprises an anionicsurfactant, a cationic surfactant, a nonionic surfactant, an amphotericsurfactant, and a catanionic surfactant, or any combination thereof.